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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

The test item was investigated for its toxicity to microorganisms following OECD 209. The test item did not inhibit respiration of activated slugde within the exposure period of 3 hours. The EC50 was estimated to be > 300 mg/L. The NOEC was determined to be 300 mg/L. The test item is considered to be not toxic to microorganisms. 

Key value for chemical safety assessment

EC50 for microorganisms:
300 mg/L
EC10 or NOEC for microorganisms:
300 mg/L

Additional information

The toxicity of the test item to microorganisms was assessed in a respiration inhibition test according to OECD 209, adopted in 1984. Five concentrations of the test substance (7.6, 19.8, 51.4, 123.2 and 300.8 mg/L) were compared to two negative controls (tap water). As positive control substance 3, 5-dichlorophenol was used and tested in three concentrations (5.0, 12.2 and 29.9 mg/L). As the test item was not soluble in water it was added directly to the samples with the activated sludge. The concentration of the freshly collected activated sludge was 1.6 g/L dry weight. The inoculum was kept aerated before the beginning of the test. After mixing the inoculum with synthetic sewage solution and appropriate amounts of control or test substances, the samples were aerated for a contact time of 3 hours at 18.5 °C. Negative controls were run as first and as last sample. After incubation the respiration rates were determined in closed bottles using an oxygen sensitive electrode. The inhibition of respiration was calculated from the respiration rates using the mean value of the negative controls as 100 %. The respiration rates of the two control samples were within 15 % of each other. The EC50 of 3, 5-dichlorophenol was in the accepted range of 5 to 30 mg/L. The test substance did not inhibit the respiration of the activated sludge. The highest obtained inhibition was 1.2 % which is less than the differences between the control samples. The EC50 was estimated to be > 300 mg/L. The NOEC was determined to be 300 mg/L.